Donald Trump, the Republican presidential nominee, with "Angel Moms," parents who say their children were killed by illegal immigrants, during a campaign event focused on immigration policy in Phoenix, Aug. 31, 2016. (New York Times)

In a major policy speech on immigration, Donald Trump criticized the government’s approach to the undocumented population, sayings the feds don’t even know the scope of the problem.

"Honestly we've been hearing that number for years. It's always 11 million. Our government has no idea. It could be 3 million. It could be 30 million," Trump said. "They have no idea what the number is. Frankly our government has no idea what they're doing on many, many fronts, folks."

Trump questioned the 11 million figure early in his presidential bid last year, and floated 30 million and 34 million as alternative estimates. That claim rates Pants on Fire.

Is it possible that, a year later, Trump’s claim of 3 million or 30 million is more accurate?

The answer is still no.

Estimating the undocumented

The U.S. Homeland Security Department last estimated the size of the undocumented immigrant population at 11.4 million in January 2012, down from a peak of 12.2 million in 2007. This count includes people who entered the United States illegally and people who overstayed their visas.

Figures from independent organizations that study immigration are all in the same ballpark. Here’s a rundown:

All of these figures come from subtracting known legal immigrants from the total number of foreign-born people documented in the U.S. census and then controlling for the estimated percentage of unauthorized immigrants who refuse to answer the census.

Researchers at all of the organizations told us Trump’s statement is wildly inaccurate.

There is "absolutely zero possibility" for the number to be just 3 million or as many as 30 million," according to Robert Warren of the Center for Migration Studies, a nonpartisan immigration policy think tank.

"There is strong evidence that the number is 11 million, with a plausible margin of error of plus or minus 1 million," he said.

Jeffrey Passel, a demographer at the Pew Research Center, called both of Trump’s numbers "virtually impossible" and explained why. On the low end, survey data shows large enough foreign-born populations and legal admissions that there could not be as few as 3 million people.

The high-end of Trump’s offered estimate is contradicted by the limited number of housing units in the United States, Mexico and Central America’s census data and surveys’ size, and U.S. data on admissions and departures.

"There’s simply no way for an additional 20 million people to be in the country and have escaped detection," Passel said.

If the figure really is as high as 30 million, school enrollment and birth registration would reflect that, as both public schooling and birthright citizenship are incentives for undocumented immigrants, pointed out Steven Camarota, research director at the Center for Immigration Studies, which advocates for low levels of legal immigrants.

"But the numbers are not out of whack," Camarota said. "Bottom line is we don’t know what the number is for sure. But based on the available evidence, it seems very unlikely that it’s 20 million (more)."

Why it’s ‘always’ 11 million

Trump suggested he was skeptical of the 11 million figure because it’s "always" been the estimate. Experts told us there’s a good explanation for that: a steady flow of people coming in and leaving.

"The reason that he has heard the same number for years is that the population has not been growing," said Warren.

"There’s enormous churn in the illegal immigration population. Hundreds of thousands come in at 11 million and then hundreds of thousands leave," Camarota said, adding that the undocumented population is a demographically unusual group as it can’t grow by births (as all children born in the United States are citizens).

But even if you folded in these citizen children, the number would be 17 million at most, he said.

While the federal estimate hasn’t been updated in a few years, experts agreed that the outside groups’ calculations are sound. Still, Camarota criticized the government for not providing a more recent figure.

"This creates enormous uncertainty in a debate about an important policy issue. It’s like saying, ‘We should do something about the deficit, but we don’t know how big it is,’ " he said. "We talk about something that everyone perceives is a problem without any data."

Our ruling

Trump said the number of illegal immigrants "could be 3 million. It could be 30 million."

Both figures are not within the range of possibility. Every credible estimate we found was in the 11 million range, with a margin of error of around 1 million. The figure has "always" been 11 million, in recent years, because of the flow of undocumented immigrants in and out of the United States.

Interview with Steven Camarota, research director at the Center for Immigration Studies, Sept. 1, 2016

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